Study Of Swept Source Based On Fiber Fabry-Perot Interferometer Tunable Filter

With the rapidly development of the absorption spectrum analysis and detection technology in various fields,so with the superiority has been recognized by more and more industries,it has important status in environmental detection,industrial production process and biomedical applications.Absorption spectra as a selective detection method in the gas absorption spectrum detection,it used the interaction characteristics between laser and gas for detection,by comparing the target gas and the spectral characteristics of the detected gas,can accurately identify the gas,and its gas concentration.In addition to differential absorption spectroscopy and Fourier transform infrared spectroscopy,a high resolution and high sensitivity technique,which is based on the absorption spectra of the swept source is more representative.Swept source can provide high speed scanning speed,wide turning range,high signal-to-noise ratio,as well as its high selectivity,are widely used in the absorption spectrum,especially in the detection of gas absorption spectra.Swept source can reduce the influence of background gas,dust,temperature and other factors.The absorption spectra can be used to improve the resolution of the spectrum with swept source,and it has a higher response rate than the traditional spectrum detection technology.Besides,the swept source can be achieved by modular design,which allow the source to change the parameters according to different needs,and suitable for fast installation and convenient maintenance in the field detection.As more studies about swept source,its advantages earned more and more attention,including the military field,the field of environmental monitoring.Therefore,swept source based on Fabry-Perot filter with narrow instantaneous linewidth laser source is the main subject of this study.The mainly study is about how to obtain a swept source with narrow instantaneous linewidth,and discuss the main factors which can affect the linewidth,including the filter bandwidth,fiber dispersion,swept rate.An all-fiber 30 KHz repetition rate swept laser source at center wavelength of 1340 nm with narrow instantaneous linewidth for swept source optical coherence tomography is reported.The swept source's output power are highly stable because of the mode locking.The phase and the intensity of this swept source are stable,bandwidth scanning range of the swept source is 10 nm,3 dB bandwidth is 6 nm,the instantaneous linewidth is less than 0.018 nm,the average output power is 9.1 mW.The swept laser source is based on Fourier-domain mode locking(FDML),uses a 5578 finesse,narrow bandwidth fiber Fabry-Perot interferometer tunable filter(FFP-TF).Spontaneous emission of the gain medium is used as background light,and passes through the long dispersion managed delay line to the FFP-TF.After filtering and parameters matching,the system can resonate and produce an ultra-stable swept laser source.At last,the factors influencing the instantaneous linewidth of the swept source were discussed.This swept laser source has high finesse which makes it suitable for highspeed molecular spectroscopy and molecular absorption spectroscopy.This paper can be divided into four parts:The first chapter is introduction,firstly introduced the background and significance of the research,including the swept source applications in various fields,the development status and related technology overview.And analyzed the various group's achievements with swept laser light source.Then it elaborated the details of the principles of swept source,and the most important performance indicators of swept source: wavelength of the source,swept rate,the output optical power,the source spectral bandwidth and instantaneous linewidth tuning.Finally it illustrates the main content and innovation topics of this paper.The second chapter introduces the design of swept source and relevant theoretical knowledge,including Fourier domain mode-locking technique,filtering principle of Fabry-Perot filter,and design a swept source system based on a narrow instantaneous linewidth Fabry-Perot filter.Besides,various factors that could affect the final output of the instantaneous linewidth of the swept source are studied,such as the long-fiber dispersion,bandwidth of the Fabry-Perot filters and swept frequency,and analyzed instantaneous linewidth variation in a scan cycle condition.And it explained and used numerical simulation to elaborated various factors affect the instantaneous linewidth of the swept source and found the optimization way.The third chapter mainly introduced the system construction and collection of the final output spectrum and experimental data.By fully understanding how the devices in need work,and their working principle,according to the experimental design of the second chapter to build up the whole swept source system platform.First thing is to collect the spontaneous emission spectra of BOA and SOA,as the theoretical basis for analysis later;secondly used a DC bias voltage loaded at FFP-TF,and check the filter transmission spectra at different DC voltages,in order to change the bias voltage so that is can be changed according to the transmission band of the filter,that can choose different central wavelengths of swept laser source;the third step is to find out the relationship between different peak to peak voltage loaded at FFP-TF and the transmission spectrum;the fourth step is to study the influence of loaded frequency at the filter on the instantaneous linewidth of the swept source;the fifth step is to setup a complete swept source platform,and collect the relevant data and build up a Michelson interferometer.Also,the results of each step were analyzed,including the BOA,SOA center wavelength can caused an effect on the test,FFP-TF at different voltages shows its scanning inconsistently,PZT deformation at different voltages,and peak-to-peak voltage can caused a different for a final swept laser's output of the instantaneous line width and optical power stability,finally found a reasonable theoretical research and analysis for even in the same system,different octave frequency swept laser source result in different spectral output signals.The fourth chapter is summary and prospect,which mainly summarizes the results of the work and prospects of swept source of this research,and propose some improvement methods and the direction of further research.